This invention relates to a process for beneficiating raw bentonite, more particularly but not exclusively naturally occurring alkaline earth metal bentonite, to produce a bentonite product of improved whiteness and purity at a higher yield than has hitherto been possible.
Much natural raw bentonite occurs in deposits which are veined by reddish-brown iron oxide. When such bentonite is mined it tends to break up into lumps of various sizes which are heavily stained on their surface by iron oxides. In order to produce a light-coloured bentonite product it is first necessary to remove this staining by a process which, for example, subjects the surface of the lumps to scraping or abrasion. The raw bentonite may also be associated with siliceous impurities such as quartz and cristobalite which must be separated from the bentonite if the product is to be useful for cosmetic or pharmaceutical compositions. British Patent Specification No. 1,143,022 (corresponding to U.S. Pat. No. 3,408,305) describes a known process for beneficiating crude alkaline earth metal bentonites. This process has the disadvantages that the yield of bentonite product is relatively low and that the product bentonite may contain up to 10% by weight of free cristobalite. The product is also not bacteriologically sterile.